feat: ez config + draft, no-pr, default-from, rerere

[dezren39]

Adds ez config list/get/set for post-init configuration.

Changes

• ez config command with list, get, set subcommands
• New config keys: draft (bool), no_pr (bool), rerere (bool) with validation
• default_from wired into ez create — when on trunk with no --from, uses config
• --no-pr flag on ez push — push without creating/updating a PR
• --no-draft flag on ez push/ez submit — override draft config
• Draft config precedence: flag > config > false
• ez init prompts to enable git rerere with rr-cache fallback
• Backward-compatible JSON deserialization (old stack.json loads fine)

Commits (6)

• 93afc5b feat: add ez config command for post-init configuration
• a834a5a feat: add draft, no_pr, rerere config keys with bool validation
• f979f00 feat: wire default_from config into ez create
• b803bde feat: add --no-pr, --no-draft flags and wire draft config into push/submit
• f4389d3 feat: add rerere prompt to ez init with fallback to rr-cache directory
• a538d55 test: add draft/no-pr resolution and stack ancestor edge case tests

Resolves #5
Resolves #7
Resolves #8
Resolves #17

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Stack (this PR is 1 of 5):

1. → feat/config ← you are here (rohoswagger#9)
2. feat/preflight (dezren39#1)
3. feat/worktree-ops (dezren39#2)
4. feat/fork (dezren39#3)
5. feat/local-merge (dezren39#4)